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`isascii'--ASCII character predicate

     #include <ctype.h>
     int isascii(int C);
`isascii' is a macro which returns non-zero when C is an ASCII
character, and 0 otherwise.  It is defined for all integer values.
   You can use a compiled subroutine instead of the macro definition by
undefining the macro using ``#undef isascii''.
`isascii' returns non-zero if the low order byte of C is in the range 0
to 127 (`0x00'-`0x7F').
`isascii' is ANSI C.
   No supporting OS subroutines are required.